the last update (monterey) changed ALL appearance screens, colors, etc., including doubling all the entries in my contacts list. I hate it. How do I change it back?

The sign-in screen is purples and pinks, my sign-in icon is now a red rose. The clashing colors are SO annoying... and that's only the start.

If you don't like the red rose, change it to something you like.

How do I get back the sign-in screen, color schemes for all screens

For the FileVault login, you cannot. For the Lock Screen, customize your Desktop Background.

un-do the doubling of ALL entries in my contacts list, etc.,

In Contacts, do you see an iCloud account and an On My Mac account. If so, select one of the accounts "All Contacts" group, select all, then delete those.

If you don't have two account types in Contacts, select "Look for Duplicates" from the Card menu and consolidate them.

After performing all from previous posting above.

MacBook Air 13″, macOS 12.1 Is that accurate ?

The current version of Monterey is 12.3.1

In good conscience, suggest performing a Time Machine Backup before updating